Thermostat



June 23, 1925. 1,542,850

A. s. CURTIS ET AL THERMOSTAT Filed March 30, 1922 //7 vemors:

A/f/ed .5. Cur/As Da via J Beaver 4 Zia W my Patented June 23, 1925.

.4 I 1,5 2,850, UNITEDSTATES PATENT 0FFlCE.f

ALFRED S. CURTIS AND DAVID J. BEAVER, 0! NEW YORK, N. Y.; SAID CURTIS AS- SIGNOB OF HIS INTEREST TO WESTERN ELECTRIC COMPANY, INCORPORATED, 01' NEW YORK, N. Y., A CORPORATION OF NEW YORK.

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Application filed larch so, 1922. Serial 1T0. 540,143.

To all whom it may concern:

Be it known that we, ALFRED STANLEY CURTIS and DAVID JOHN BEAVER, citizens of the United States, residing at New York, in the county of New York, State of New York, and New York, in the county of New York, State of New York, respectively, have invented certain new and useful Improvements in Thermostats, of which the following is a full, clear, concise, and exact description.

This invention relates to an electrical control device and pertains more especially to a thermostat.

In thermostats for controlling the temperture of a supply of liquid ithas been customary to immerse in the liquid a thermosensitive device having a pair of contact members, one of which is movable relative to the other. These contact members are connected with a source of electrical energy through a relay adapted to be energized upon the closing of the contacts. The relay serves to control the means for heating the liquid. A comparatively heavy current is necessary in order to energize the relay and because of the inductance of the relay, sparking occurs between the electrodes when the circuit is opened. The continued sparking causes the deterioration of the electrodes and thereby lowers the efliciency of the device.

It is an object of this invention to prevent sparking between the contact members of a.

thermo-sensitive device when they are separating to break .a circuit. More particularly, it is an object of the invention to utilize extremely small currents to accomplish the. opertion of a relay.

These objects are accomplished by arranging the thermo-sensitive means in the input circuit of an am lifier, such, for example, as a vacuum tu c and arranging the rela in the output circuit thereof. An extreme y slight current in the input circuit is effective to cause the operation of the relay. Sparking between the contact members of the thermo-sensitive device is prevented due to the small current used and to the absence of inductance in the input circuit.

This invention will be better understood by having reference to the following specification and accompanying drawing wherein the invention is disclosed diagrammatically.

A supply of liquid 10, the temperature of 'erator.

which is to be controlled, is contained in a vessel 11, heated by means of the lamps 12 wlilch are supplied with electrical energy from the source 13, preferably a D. C: gen- The movable contact 14 of relay 15 is included in the circuit between the source 13 and the lamps 12 and controls the flow of current in this circuit. 7 The annode 16 of the vacuum tube 17 is connected to the positive side of the source 13 through the winding of the relay 15. The cathode 18 of the vacuum tube is in circuit with the source 13, one terminal of the cathode being connected to the positive side of the source 13 through the resistance 19 and the other terminal to the negative side of the source through the resistance 20. The negative terminal of the cathode 18 is connected to the grid 21 of the vacuum tube by means of the resistance 22. The grid is alsoconnected with the electrode 23 of a mercury thermometer 24, which is immersed in the liquid 10. The mercury 25 in the thermometer is eonnected to the negative side of the source This device may be operated from a lighting circuit of 110 volts in which event the source 13 is the lighting circuit. When operated from such a circuit the resistances 19 and 20 are of the order of several ohms dependent upon the filament current necessary for the particular vacuum tube used, the re sistance 19 being greater than the resistance current in the output circuit is of suflicient I strength to maintain the relay energized to hold the contact 14 in position to close the circuit through the lamps 12. As the temperature of the liquid increases the mercury 25 rises in the thermometer and establishes contact between it and the electrode23, thus closing the circuit and reducing the potential of the grid to that of the negative side of the source of energy. The cathode 18 is at a potential greater than that of the nega tive side of the source of energy because of the potential drop in the resistance 20. The grid is therefore negative with respect to the cathode and the space current is correspondingly weakened. The relay 15 is deenergized and the contact 14 moves to a position to open the circuit through the lamps and the liquid then begins to cool. As soon as the mercury drops sufiiciently to break the contact between it and the electrode 23, the grid and cathode again become of the same potential and the space current increases, thereby recnergizing the relay 15 and causing the contact 1a to again close the circuit through the lamps 12. These operations are continuously repeated and the liquid maintained at the desired temperature.

Because of the extremely high value of the resistance 22, the current flowing in the input circuit when the mercury is in contact with the electrode 23 is very minute, being for example, less than 10'6 amperes and as the resistance 22 is non-inductive, there is no sparking between the mercury 25 and the electrode 28. The resistance 20 serves to maintain the cathode at a potential higher than the negative side of the source of electrical energy thereby establishing the difierence of potential necessary to make the grid negative with respect to the cathode when the mercury is in contact with the electrode 23.

Although the invention has been described in connection with a thermostat for controlling the temperature of a liquid it is obvious that it is applicable to other types of thermostats employed for other uses. In certain of its aspects the invention, as will be apparent from the appended claims, is not limited to use in connection with thermally controlled devices.

What is claimed is:

1. In a device of the character described, an amplifier, thermo-sensitive means in the input circuit thereof for opening and closing the same, and a heat supply controlling device in the output circuit operable upon change of current in said circuit.

2. In combination, an electric discharge device having a cathode, an anode, and a control electrode, a source of electrical energy, connections from said source for supplying heating current to the cathode and for maintaining a potential difference between the cathode and the anode, means for normally maintaining the control electrode at approximately the same potential as the cathode, and means for rendering the control electrode negative with respect to the cathode, said last mentioned means comprising a source of direct electromotive force.

3. Apparatus for controlling temperature comprising a source of heat, a vacuum tube for controlling said source and thermosensitive means in the input circuit of said vacuum tube.

4. In combination, an electric discharge device having a cathode,'grid, and anode,

an input circuit comprising a source of electrical energy connected between said grid and cathode, means to open and close said circuit, means to maintain said grid and cathode at a common potential when the input circuit is open, and means in the output circuit operable upon change of space current.

5. In combination, an electric discharge device having a cathode and a grid, an input circuit having therein a source of electrical energy, means to open and close said circuit, means to maintain said grid and cathode at a common potential when said circuit is open, and means to vary the potential of the grid relative to the cathode when said circuit is closed.

6. In combination, an electric discharge device having a grid and a cathode, mea.1s for normally maintaining said rid and cathode at the same potential, tiermally controlled means to render the grid negative with respect to the cathode, and means in the output circuit operable upon change of space current.

7. In combination, an electric discharge device having a cathode, grid, and anode, an input circuit comprising a source of electrical energy connected between said grid and cathode, thermo-sensitive means to open and close said circuit, means to maintain said grid and cathode at a common potential when the input circuit is 0 en, and means in the output circuit opera le upon change of space current.

8. In combination, an electric discharge device having a cathode and grid, an input circuit having a source of electrical energy therein, thermo-sensitive means to open and close said circuit, means to maintain the grid and cathode at a common potential and means to vary the potential of the grid relative to the cathode.

9. In a device of the character described, an amplifier, thermal means in the input circuit for opening and closing the same, and means in the output circuit operable upon variation of the space current.

10. In combination, an electric discharge device having input and output circuits, an electrical device, means in said output circuit for controlling said last mentioned device, switching means in said input circuit for controlling the operation of said discharge device, and a common source for supplying electrical energy to the cathode, the input and output circuits and said second mentioned electrical device.

11. A device of the character described comprising an electric discharge device having a cathode, grid, and anode, input and output circuits, means in said output circuit and cathode at the same potential when the input circuit is o n.

12. A device 0 the character described comprisin an electric dischar e device having a cat ode, grid, and ano e, input and output circuits, a heating supply controlling device in the output circuit operable upon variation of the space current, thermo-sensitive means for opening and closing the inputcircuit, and means to maintain said grid and cathode at 'the same potential when the input circuit is open.

13. A device of the character described comprising an electric dischar e device hav-' ing a cathode, grid, and ano e, input and output circuits, means in said output circuit operable upon change of/the space current, means for opening said input circuit, and

an electric connection between said grid and cathode for maintaining said electrodes at a common potential when the input circuit is 14. A device of the character described comprising an electric dischar e device having a cathode, grid, and ano e, input and output circuits, means in said output circuit operableupon variation of the space a current, means for opening said input circuit, and a resistance connected between said grid and cathode whereby they are maintained at a common potential when the input circuit is open.

15. A device of the character described comprising an electric discharge device having a cathode, grid, and anode, input and output circuits, a heat supply controlling device in the output circuit operable upon variation of the space current, thermo-sensitive means in the inputcircuit for opening and closing the same, and an electric con nection between said grid and the cathode.

16. A device of the character described comprising an electric discharge device having a cathode, grid, and anode, input and output circuits, a heat supply controlling device in sald output circuit operable upon variation of the space current, thermo-sensitive means for opening and closing said input circuit, and a resistance connected between said grid and cathodewhereby said electrodes are maintained at a common potential when the input circuit is open.-

17. In combination, a vacuum tube having a grid, a cathode, and anode, a source heating member controlled by said relay and connections from said heatingmember to said source of electrical energy.

18. In combination, an electrlc discharge device having a cathode, grid, and anode, a source of electrical ener connections from said source for su plying heating current to said cathode and for maintain a poten t-ial difference between said cat iode and anode, means for maintaining a normal potential relation between said grid and cathode, and switching means for varying said relation. 19. In combination, an electric dischar e device having a cathode, id, and ano e, thermal means to open and close the input circuit thereof, means for maintaining a potential relationbetween said grid and cathode when said circuit is open, means to change said relation when said circuit is close and means in the output circuit operable upon change of space current.

20. In combination, an electric discharge device having a cathode, grid, and anode, an input circuit having therein a source of electrical energy, thermal means to open and.

close said circuit, and means to maintain a pptential relation between said grid and cat ode when said circuit is'open,sa1d source being effective to vary said relation when the circuit is closed.f g

21. In combination, an electric dischar e device having a cathode, grid, and ano e, means for maintaining a normal potential relation between said grid and cathode, thermally controlled means to vary said potential relation, and means in the output circuit operable upon change of space current.

22. In combination, an electric discharge device having a cathode, grid, and anode, an input circuit comprising a source of electrical energy connected between said grid and cathode, thermally sensitive means to open and close said circuit, means to maintain a potential relation between said grid and cathode when the input circuit is open, said source being effective to vary said relation when said circuit is closed, and means in the output circuit operable upon change of space current.

23. A device of the character described, comprising an electric discharge device having a cathode, grid, and anode, input and output circuits, means in the output circuit operable upon change of space current, thermally sensitive means for opening and closing the input circuit, an electrical connection between said grid and cathode comprising means for maintaining a potential relation between said electrodes when the input circuit is open and means for varying said relation when the input circuit is closed.

24. In combination, a source of voltage comprised in a circuit having an impednnce hf the order of several megohms, a sensitive means in the input circuit, of said thermally controlled switch in end 'clrcuit, amplifier.

and a device responsive to an effect pro- In witness whereof, we hereunto subscribe 10 duccd in said circuit. our names this 27th day of March, A. D.,

25. Apparatus for controlling tempera- 1922.

ture comprising a source of heat, an'ampli- DAVID J. BEAVER. Iier for controlling said source, and thermo- ALFRED S. CURTIS. 

